We propose to develop a new generation of clinical assays which are noninvasive and analyze for multiple components simultaneously. Our strategy is based on the observation that light from the Near Infrared (NIR) region of the electromagnetic spectrum can penetrate human tissue to a marked degree. At the same time, virtually all molecules of biochemical interest exhibit weak, but distinctive absorption bands in this region. In order to exploit this "spectroscopic window" into human tissue, we propose to take advantage of recent advances in optical components and transducers which will make possible the measurement of very weak absorbances against a large scattering background. In addition, we will employ new concepts in multivariate statistics to aid in interpreting the multiple, overlapping absorption bands. Our confidence that a new class of non-invasive assays can be developed is based upon the recent, successful application of Near Infrared Analysis (NIRA) to a wide spectrum of agricultural products. Our research plan involves performing exacting spectroscopic measurements of excised human tissue and blood followed by a detailed interpretation in terms of the spectra of the constituent biochemicals such as protein, lipid, collagen, hemoglobin, etc. With this basic knowledge in hand, we will then attempt to measure the NIR spectra of live human subjects with the aid of fiber optic light guides. We propose to take advantage of the time dependent nature of the signals which arise from arterial blood flow to separate tissue and arterial signals. Quantitative, simultaneous assays for arterial oxy/deoxy hemoglobin ratio, hematocrit and tissue hydration will be developed.